Treatments for type II (non-insulin dependent) diabetes are currently centered on hypoglycemic agents. Strict blood glucose control clearly lowers rates of transition to complications and mortality rates. The major hypoglycemic agents used are insulin preparations or oral hypoglycemic agents such as sulfonylurea agents, thiazolidine derivatives, α-glucosidase inhibitors, biguanide agents and the like. Among such oral hypoglycemic agents, biguanide agents are known to be the most effective in type II diabetic patients. Numerous biguanide derivatives have been synthesized to date, and the hypoglycemic actions of various biguanide derivatives have been reported in publications such as, for example, J. Am. Chem. Soc., 81, 3728-3736 (1959). However, such biguanide derivatives are commonly recognized as having the potential to induce lactic acidosis, and even the aforementioned publications have not confirmed the presence or degree of blood lactic acid level augmenting effects of biguanide derivatives. Consequently, the existing biguanide agents, such as metformin, have been contraindicated for diabetic patients with anamnesis of lactic acidosis, diabetic patients with kidney dysfunction, diabetic patients with liver dysfunction, diabetic patients with cardiovascular dysfunction, diabetic patients with pulmonary dysfunction, diabetic patients susceptible to hypoxia, diabetic patients consuming excessive alcohol, diabetic patients with gastrointestinal disturbance and elderly diabetic patients, due to the risk of their causing lactic acidosis (DRUGS in JAPAN : Ethical Drugs, 23rd edition, p.2094, 2000, Japan Pharmaceutical Information Center).
In addition, approximately 10% of type II diabetic patients are said to have overt nephropathy, therefore many patients cannot take biguanide agents. Sulfonylurea agents, thiazolidine derivatives and insulin preparations are administered in such cases, but because these agents produce a hunger craving and thus tend to result in increased body weight, such agents cannot be considered suitable for obese diabetic patients. A demand therefore exists for biguanide agents which lower blood glucose substantially without increasing blood lactic acid levels, in order to reduce the risk of inducing lactic acidosis.